The present invention relates to an anti-glare covering for illuminate switch or indicator or, more particularly, to an anti-glare key-top covering for illuminate switch installed, for example, in the room of an automobile capable of ensuring good visibility to the viewer and preventing the illuminate switch from being mirror-imaged on the windowpane and the like.
It is very common in recent years that various illuminate switches and illuminate indicators are used in the room of automobiles, aircrafts, vessels and the like as on the dashboard of a car. The covering of such an illuminate switch or indicator bears letters, symbols, patterns and the like thereon for indication and has a light source below by which the covering is illuminated from behind so as to give good visibility of the indication letters and the like to the viewer. It is important from the standpoint of safety of driving that the covering for such an illuminate switch or indicator is anti-glaring which means that any extraneous external light can be shielded by permitting the light from inside to be transmitted therethrough as completely as possible and that the illuminate switch or indicator per se is prevented from mirror-imaged on the windowpane.
One of the most convenient and effective ways to render such a cover anti-glaring is to use an anti-glare microlouver sheet for constructing the top portion of the covering, which is illuminated with a light from behind. The anti-glare microlouver sheet here implied is illustrated in FIG. 1 by a cross sectional view, which is a sheet 1 composed of alternate stripes or layers of transparent portions 2 and deeply colored or opaque portions 3 in a microscopically fine louver-like fashion, optionally, provided with surface-protecting films 4 on at least one surface thereof. The above described anti-glare microlouver sheet is made from a plastic resin such as a cellulose acetate butyrate or a rubbery elastomer such as a silicone rubber.
FIG. 2 illustrates a cross sectional view of a typical conventional anti-glare covering an anti-glare microlouver sheet 21 composed of alternately arranged stripes of transparent silicone rubber layers 22 and colored silicone rubber layers 23. The anti-glare microlouver sheet 21 is mounted above the opening 28 at the top portion of a key-top cover 24 in the recessed cavity 25 by adhesively bonding with an adhesive 26. The anti-glare sheet 21 is illuminated from behind with a lamp 29 so as to give glare-free visibility to the eyes viewing from above. The anti-glare covering illustrated in FIG. 2 is not always quite satisfactory due to several problems and disadvantages. For example, the anti-glare sheet 21 is adhesively bonded to the covering member 24 with the adhesive 26 only on a very limited surface area so that the anti-glare microlouver sheet 21 sometimes falls from the position by failure of adhesion. When it is intended to solve this problem by increasing the area available for adhesive bonding, the effective area of the anti-glare sheet 21 is correspondingly decreased to affect the visibility of the switch or indicator so that the versatility in the design of the top portion of the covering member 24 is very limited. Since the anti-glare sheet 21 is mounted in the recessed cavity 25 on the top portion of the covering member 24, in addition, a gap space 27 is unavoidably formed around the anti-glare sheet 21 and dusts and finger filths are deposited in this gap space 27 in the long run of use to cause a problem in the hygiene and beautiful appearance. An anti-glare microlouver sheet made from a silicone rubber has low rigidity and is poorly resistant against compressive force so that it is sometimes unavoidable that the sheet under hot-pressing is deformed and the view angle of the micrlouvers is uncontrollably changed. When the anti-glare microlouver sheet is formed from a cellulose acetate butyrate, the sheet is sometimes deformed or emits unpleasant odor in the course of preparation thereof by hot-pressing due to the low heat resistance of the material.
The anti-glare covering of an illuminate indicator in the prior art illustrated in FIG. 2 is also disadvantageous in respect of the relatively low light transmission so that, especially when the letters and patterns for indication below the anti-glare sheet are provided at a distance from the top plate of the covering, the visibility of the letters and patterns is poor under daylight leading to occurrence of shades of the illuminated portion. Although this problem can be partly solved by providing the upper surface thereof with a white coating, this means is not practical due to the loss in both of the visibility and anti-glaring effect as a consequence of the irregular diffusion of light by the particles of the white pigment.